In data unit based communication, i.e. in which an information to be transmitted is divided into a plurality of units, and the individual units are sent over a communication network, it is known to provide queue buffers at links along the network, such that data units transported over such a link may be buffered. The buffer may be a sending or output buffer (i.e. a buffer for data units that are to be sent over the outgoing link) or a receiving or input buffer (i.e. a buffer for data units that have been sent over the incoming link).
Such units for transporting data may carry a variety of names, such as protocol data units, frames, packets, segments, cells, etc., depending on the specific context, the specific protocol used and certain other conventions. In the context of the present document, all such units of data shall generically be referred to as data units.
The procedures for placing data units into a queue, advancing them in the queue, and removing data units from the queue are referred to as queue management or queue control.
Many concepts of queue management are known, including such concepts in which a queue length parameter (e.g. the absolute length of queue or an average length) is monitored and compared with a length threshold value, in order to perform a congestion notification procedure if the threshold value is exceeded. Such a congestion notification procedure can consist in dropping a data unit and/or in marking data units (e.g. setting a congestion notification flag in data units). Various examples for such management concepts, like drop-on-full or random early detection (RED) are described in the introduction of EP-A-1 249 972. As a consequence, a repetition is not necessary here.
EP-A-1 249 972 proposes a scheme in which the length threshold value that is to be compared with the queue length parameter is automatically updated on the basis of one or more characteristics of the link over which the queued data units are to be sent. By adapting the automatic threshold to one or more link characteristics, a very flexible form of active queue management is obtained that may provide improved throughput and reduced delay, especially over links that have time varying characteristics such as wireless links. Thereby data unit handling is improved with respect to systems known before.